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When rays are incident on a boundary between medium, a section of incident waves goes back into the initial medium while the remaining is sectionaly absorbed and sectionaly transferred into the second medium.
(1) Rarer and denser medium : A medium is called denser if the velocity of ray in that phase is less than the speed of the wave in other phase.
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In comparison to air velocity of sound is largest in water, hence water is rarer phase for sound waves w.r.t. air. But it is not right for light (EM-waves). For light rays water is denser medium w.r.t. air.
(2) In refraction or reflection frequency remains fixed
(3) For reflection angle of incidence (i) = Angle of reflection (r)
(4) In part of refraction or transmission sini/sint = vi/vt
(5) Boundary conditions: Reflection of ray pulse from some boundary relays on the nature of the boundary.
(i) Rigid end : When the incident ray arrives a fixed end, it exerts an upward pull on the side, according to Newton's law the same end exerts an similar and opposite down ward tension on the string. It gives result an inverted pulse or phase change of p.
Crest (C) reflects as trough (T) and vice-versa, Time denotes as by T/2 and Path changes by λ/2
(ii) Free end: When a pulse is reflected from a free side, then there is no modification of medium.
Crest (C) denotes as crest (C) and trough (T) denotes as trough (T), Time modifies by zero and Path modifies by zero.
(iii) Exception : Longitudinal pressure pulse suffer no modification in phase from dead end i.e. compression pulse reflects as compression ray. On the other hand if longitudinal pressure ray reflects from last end, it suffer a medium change of p i.e. compression denotes as rarefaction and vice-versa.
(iv) Effect on different variables : In case of reflection , because phase is similar and hence, wavelength l, frequency (ω) and speed do not modifies. On the other hand in case of transmitted pulse since medium modifies and hence velocity wavelength (or k) modifies but frequency (ω) remains the same.
6. Wave in a combination of string
(i) Wave goes from rarer to denser medium
(ii) Wave goes from denser to rarer medium
(iii) Ratio of amplitudes : It is shown as follows
Echo:
An echo is simply the retransmission of speaker's own voice caused by reflection at a distance surface.
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If there is a sound reflector at a distance d from host, then the time interval between original source and it's echo at the site of source will be
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As the persistence of hearing for person ear is 0.1 sec, therefore in order that an echo of short sound (e.g. clap or gun fire) will be heard if t > 0.1 => 2d/v>0.1 => d>v/20
If v ¾ speed of sound ¾ 340 m/s then d > 17 m.
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